The present invention relates to the field of grid reinforced concrete bridge decks or grating, and, more particularly, to an improved form pan device for use with half-depth bridge decks or the like which enables mechanical locking of the form pan in its desired position.
Grid reinforced concrete bridge decks have been used in the past with significant success in that they provide a strong and relatively light weight deck compared to other types of bridge decking. Precast panels of grid reinforced concrete are far lighter and much stiffer than equivalent rebar reinforced slabs. A square foot of grid reinforced concrete deck weighs about half that of a one square foot of conventional, eight-inch, rebar reinforced deck. Field experience has shown that it is reasonable to expect at least a fifty-year life from a properly installed grid reinforced concrete deck. While the initial cost of a grid reinforced concrete deck may be somewhat higher than a rebar reinforced slab deck, it can be expected to last two or three times as long.
Grid reinforced concrete decks or gratings are shown, for example, in the patents to Greulich Nos. 2,089,891, 2,275,104 and 2,275,105. The procedure used in assembling these type of gratings is to space a plurality of main longitudinal beams, having slots therein spaced along the longitudinal axis thereof, a certain distance apart from one another with their slots aligned, insert a plurality cross bars transversely through the aligned slots while in a flat position relative to the main beams, and then turn the cross bars in the slots approximately 90 degrees to an upright position, thereby locking the main beams and cross bars together to form a rigid structure. Thereafter, tertiary longitudinal bars and/or rebars can be added intermediate the main beams. The cross bars may be fabricated with holes therein for receiving the rebars and complementary slots therein for receiving the tertiary bars.
Concrete form pans are provided under the grid formed by the beams and cross bars to enable the grid to be top-filled with concrete, thereby producing a grid reinforced concrete deck. In addition to its use on bridges, these type of decks can be used where any reinforced heavy duty flooring is desired, such as subway covers, vault covers, loading platforms and the like.
In one particular type of grid reinforced concrete deck, to which the instant invention is directed, only half the depth of the main beams is filled with concrete. This type of deck is known as a "half-depth" deck. The half-depth deck is made by positioning a concrete form pan under the cross bars at a mid-point on the height of the main beams, thereby enabling concrete to be top-filled into the grating, which results in a concrete thickness which is only half the height of the main beams. For example, if five inch main beams are used the resulting concrete thickness of a half-depth deck would be approximately two and one-half inches. Half-depth decks are preferred for certain application where it is desired to have a lighter weight deck than would otherwise result from filing the entire beam height with concrete.
Typically, the main beams include a center flange which extends along the length thereof and is used to support the form pan when making half-depth decks. Conventional form pans used in half-depth decks are flat pans having side portions intended to rest on the center flanges of two adjacent main beams, respectively. The bottom edge of the cross bars, when rotated upright in the main beam slots, do not contact the pan, but are spaced a certain distance therefrom, the amount of space depending on the height of the cross bars. Inasmuch as only the weight of the pan holds it in place on the center flanges, it is often necessary to tack weld the pan to the flanges to prevent movement thereof. Tack welding the form pans is time consuming, increases the manufacturing cost of the grid and causes undesirable warping which often allows liquid to seep beneath the center flanges. Tack welding the pan to the beam may also set up stress in the grid assembly which may cause early metal fatigue and the welds to fail. It will be apparent to those skilled in the art that a warped pan may prevent the edge thereof from forming a good seal with the central flange on the main beams. As a result, when the grid is top-filled with concrete the concrete may leak before it sets between the edge of the pan and the central flange. Leaking of the concrete is undesirable in that it requires additional labor to clean surfaces on which it leaks prior to the surfaces being painted. In addition, in bridge construction leaking concrete can cause a hazardous situation in areas below the grid when it is being top-filled with concrete. Further, if top-filling is carried out on a bridge over water, a pan which leaks concrete could result in an environmentally unsound condition requiring special precautions to comply with EPA requirements. While a sealer can be used to help prevent leaks at the edges of the pan, sealing all of the pan edges is labor intensive and increases the costs associated with manufacturing the grid.
Thus, a need exists for an improved form pan for half-depth concrete reinforced decks which avoids tack welding in its desired position, and which forms a good seal at the edges thereof with the flanges on the main beams.